1. Field of the Invention
The present invention relates in general to combustion methods and apparatus, and in particular, to methods and apparatus for combusting a fuel with an oxidant, preferably an oxygen-enriched oxidant, in high particulate and/or high volatiles environments.
2. Related Art
Combustion burners of the type illustrated in U.S. Pat. Nos. 5,975,886 and 6,068,468, known under the trade designation xe2x80x9cALGLASS FCxe2x80x9d (trademark) have been highly successful in design and are in operation worldwide in a multitude of glass furnaces for producing glass items. However, end users and combustion scientists are always seeking improvements. In certain targeted extreme conditions, where the glass furnace combustion environment is characterized by a large amount of volatiles, the volatiles can cause problems in operation of the burners. For example, the volatiles leave the glass batch in a gaseous form, together with additional particulates entrained in the gas space of the furnace. The volatiles are typically brought into contact with a furnace crown, where they condense, due to the colder wall temperature, and eventually run down the crown back into the molten glass batch. When a relatively colder fluid stream of oxidant and/or fuel comes in contact with a liquid phase falling down the furnace wall, the relatively colder fluid stream promotes solidification of the liquid phase, leading to the gradual obstruction of burner orifices. This in turn may lead to a deterioration of the combustion process, and finally to block/burner tip damage. The condensation of the particulate, volatile matter may also produce block corrosion, particularly at low temperatures.
The patterns described above are primarily above the molten batch area. Further downstream in the glass furnace, particularly those with high volatile content, the volatiles close to the burner are recirculated toward the burner, where they will typically condense on the front face of the burner, and then solidify in the proximity of cold spots on the front face of the burner.
FIG. 1 illustrates schematically a temperature profile for a conventional burner block 1 available from Air Liquide under the trade designation ALGLASS FC(trademark), as predicted by Fluent computational fluid dynamics (CFD) software. In this simulation, a major portion of total oxygen was injected at ambient temperature, and exited through two upper orifices, 3(a) and 3(b), heated only by the warm burner block. In this simulation, a fuel, natural gas, was injected in the burner and exits three lower orifices 5(a), 5(b), 5(c). The front face of the burner block is designated as 20. It is noted that the temperature of front face 20 around the oxygen injectors and in some areas around the left-most fuel injector 5(c) was significantly lower than the temperature elsewhere on the face of the burner block. This is indicated by the hatched areas 7 in FIG. 1. The computer simulation indicated that the area 7 had the lowest temperature on the front face 20 of burner block 1, this temperature being around 800K. This temperature is well below solidification temperature of glass, and is also much lower than the solidification temperature of volatile matter in the combustion environment above the glass.
In FIG. 1, the two orifices 3(a) and 3(b) supplied the bulk of the oxygen necessary to combust the natural gas exiting orifices 5(a), 5(b) and 5(c). The gas exiting the three natural gas orifices 5(a), 5(b) and 5(c) contained, besides the natural gas fuel, from about 5 to about 20% of the total oxygen as well, allowing for some combustion to be initiated in the burner block. Thus, as predicted by this simulation, the temperature of the burner block/gas mixture at the fuel injector level was significantly higher, and the solidification process noted at the oxidant injector level was not observed.
FIG. 1 also illustrates an interesting phenomenon, namely the non-symmetry of the flow out of the symmetrical burner block. While the two oxygen orifices 3(a) and 3(b), and the three natural gas orifices 5(a), 5(b), and 5(c) were placed symmetrically, it should be noted that the left-hand side of the burner face 20 was colder when compared to the right-hand side. This trend was attributed to the slightly non-symmetrical combustion chamber, leading to different flow patterns in the combustion chamber. This observation is validated in the field, where the different injectors display different flame/flow patterns.
It would be an advance in the burner art if burner operation could be improved in high particulate, and/or high volatiles environments to prevent solidification of the particulates and/or volatiles on the face of the burner blocks.
A first aspect of the invention is an apparatus for combusting a fuel with an oxidant, the apparatus comprising:
(a) a ceramic burner block, the burner block having a back face and a front face, the burner block having at least one oxidant cavity in an upper portion of the burner block, and at least one fuel cavity in a lower portion of the burner block, each cavity extending from the back face to the front face; and
(b) the at least one oxidant cavity having positioned therein a fuel supply conduit, the fuel supply conduit having a fuel supply conduit exit positioned a sufficient distance from the front face to allow combustion of at least a portion of fuel exiting the fuel supply conduit exit with at least some of the oxidant traversing the oxidant cavity, and the least one fuel cavity having connected thereto, near the back face, an oxidant conduit, thereby allowing mixing of a minor portion of the oxidant with the fuel.
Preferred are apparatus of the invention wherein the fuel supply conduit is connected near the back face to a fuel supply manifold; apparatus wherein the at least one fuel cavity is connected near the back face to a fuel supply manifold; and apparatus wherein the at least one fuel cavity is connected near the back face to the fuel supply manifold.
Particularly preferred apparatus of the invention are those having two oxidant cavities positioned in the upper portion of the burner block, and three fuel cavities positioned in the lower portion of the burner block, wherein each of the two oxidant cavities has positioned therein one of the fuel supply conduits.
A second aspect of the invention is a method of combusting a fuel with an oxidant, the method comprising the step of supplying the apparatus of the invention with a fuel and an oxidant, at least a portion of a total amount of the oxidant routed to the fuel supply cavity, and at least a portion of the fuel routed to the oxidant cavity.
Preferred are methods of combusting a fuel with an oxidant, wherein a major portion of the fuel is supplied in three fuel cavities, and a major portion of oxidant is supplied via two oxidant cavities.
A third aspect of the invention is a method of heating a charge in a high volatiles environment, the method comprising the steps of supplying an apparatus of the invention with a fuel and an oxidant, at least a portion of a total amount of the oxidant routed to the at least one fuel cavity, and at least a portion of a total amount of the fuel is routed to the at least one oxidant cavity.
Preferred are methods of heating a charge in a high volatiles environment, wherein a major portion of the fuel is supplied in three fuel cavities, and a major portion of oxidant is supplied via two oxidant cavities.
Also preferred are methods wherein there are a plurality of burner blocks, each of the burner blocks spaced apart by a distance D, and wherein there is positioned an oxygen lance a distance of approximately one-half D and positioned between each of the plurality of burner blocks.
Further understanding of the invention may be had by review of the following description and claims.